1. Field of the Invention
The present invention relates to photoconductors for electrophotography, and particularly to a photoconductor for electrophotography which contains a squarylium compound in the photosensitie layer thereof formed on an electroconductive substrate.
2. Description of the Prior Art
Photosensitie materials which have heretofore been used in photoconductors for electrophotography include inorganic photoconductive substances such as selenium and selenium alloys, dispersions of inorganic photoconductive substances such as zinc oxide and cadmium sulfide in resin binders, organic polymeric photoconductive substances such as poly-N-vinylcarbazole and polyvinylanthracene, organic photoconductive substances such as phthalocyanine compounds and disazo compounds, and dispersions of such organic polymeric photoconductive substances in resin binder and films of organic photoconductive substance as mentioned above, deposited by means of vacuum evaporation.
Photoconductors are required to have a function of maintaining a surface electric charge in the dark, a function of generating an electric charge upon receiving light, and a function of transporting an electric charge upon receiving light. They are classified into two types of photoconductors, namely so-called monolayer type photoconductors, and so-called laminate type photoconductors. The former comprises a single layer having all of the above-mentioned three functions, and the latter comprises functionally distinguishable laminated layers, one of which contributes mainly to the generation of electric charge, and another of which contributes to the retention of surface electric charge in the dark and the electric charge transportation upon receiving light. In an electrophotographic method using a photoconductor of the kind as mentioned above, for example, the Carlson's system is applied to image formation. The image formation according to this system comprises steps of subjecting a photoconductor in the dark to corona discharge to charge the photoconductor, exposing the surface of the charged photoconductor with imagewise light based on a manuscript or copy bearing, e.g., letters and/or pictures to form a latent electrostatic image, developing the formed latent electrostatic image with a toner, and transferring the developed toner image to a support such as a paper sheet to fix the toner image on the support. After the toner image transfer, the photoconductor is subjected to the steps of removal of the electric charge, removal of the remaining toner (cleaning), neutralizaiton of the residual charge with light (erasion), and so on to be ready for reuse.
Photoconductors for electrophotography in which use is made of an organic materials(s) have recently been put into practical use by virtue of the advantageous feature(s) of flexibility, thermal stability, and/or a film forming capacity. They include a photoconductor comprising poly-N-vinylcarbazole and 2,4,7-trinitrofluoren-9-one (disclosed in U.S. Pat. No. 3,484,237), a photoconductor using an organic pigment as a main component (disclosed in Japanese patent laid-open No. 37,543/1972), and a photoconductor using as a main component a eutectic complex composed of a dye and a resin (disclosed in Japanese patent laid-open No. 10,785/1975). A number of novel hydrazone compounds and disazo compounds and the like have also been put into practical use for photoconductors.
Although organic materials have many advantageous features mentioned above wtih which inorganic materials are not endowed, however, the fact is that there have been obtained no organic materials fully satisfying all the characteristics required of a material to be used in photoconductors for electrophotography at the present. Particular problems involved in organic materials have been concerned with photosensitivity and characteristics in continuous repeated use.